One scenario holds that the Hunley was swamped by or struck by a Union vessel. Or that it plunged to the seafloor to avoid detection and never made it back up. A latch on theforward conning towerwas found to be ajar.

The Hunley's "torpedo" was attached to a spar. The crew embedded it in the Housatonic's hull, and the charge was detonated. It's possible the sub's hull was breached by the explosion or the men were rendered unconscious at some point.

Nearly all of the human remains were found where the men were at their stations, rather than jammed together at an escape hatch. The remains were buried in 2004.

Work on the Hunley will continue for at least another five to seven years.

Conservators have concentrated on painstakingly removing the sediment -- or concretion -- that was firmly attached to the Hunley's exterior and cramped interior.

After the process is finished, the submarine will be moved to a museum for display, though details have not been worked out.